Oct. i, igao Fusarium-B light (Scab) of Wheat and Other Cereals g 



organism. The conidial masses tend to be more dense in the cases of 

 infection by Fusarium herbarum and F. avenaceum and less so in the 

 case of infection by Gibberella saubinetii and other Fusarium species. 

 Because of the fact that at the bases of the spikelets moisture from rain 

 or dew is held for a considerable length of time, the conidia are usually 

 formed here, extending along the furrow formed at the line where the 

 inner and outer glumes meet. In cases where the infection extends 

 down to the upper node, conidia may be produced on the node also. 

 They never form pionnotes but usually produce small sporodochia, 

 which are generally abnormal in size and shape. 



Rye. — The symptoms of headblighting of rye are very much like 

 those of wheat, except that the water-soaked appearance is not so 

 prominent. The infection seldom extends as far down as the second 

 node before the plant naturally matures. Conidia are usually formed 

 only at the bases of the spikelets and in the furrow formed where the 

 inner and outer glumes meet and, to some extent, under the outer glumes. 

 In moist weather, however, conidia may be formed throughout the 

 infected area. Heads infected and killed at an early stage remain 

 straight, while normal heads are slightly bent. 



Barley. — The symptoms of blight on barley heads are usually 

 different from those on wheat and rye, seldom resembling those on the 

 latter. Usually only one kernel is killed, or occasionally several kernels 

 in one row. In some cases the three kernels forming a spikelet are 

 attacked and later, if conditions are favorable, the rest of the head is 

 blighted. The first sign of infection is a small, water-soaked, somewhat 

 brownish spot appearing at the base or the middle of the glume or on the 

 rachis. The water soaking and browning spread in all directions from the 

 point of infection, soon including the whole glume, the whole spikelet, or 

 several spikelets, but the infection is by no means as uniform as it is in 

 wheat and rye. 



Oats. — The symptoms of headblighting of oats resemble those of 

 wheat. Because of the structure of the panicle, however, the infection is 

 usually restricted to one spikelet and is therefore not so conspicuous as 

 it is in wheat or rye. 



LIFE HISTORY OF THE CAUSAL ORGANISM IN RELATION TO 



PATHOGENESIS 



The life history of the parasite, so far as it is connected with that of 

 the hosts, has been followed by the writer through the entire year, and 

 is here briefly outlined. 



PRODUCTION OF SPORES 

 CONIDIA 



Production of conidia upon the host plant is more or less common in 

 all forms of Fusarium attacks on cereals. In many cases it may be 

 so abundant that it leaves no doubt as to the real source of inoculum for 

 subsequent infection in nature. 



